SAW Response from Acoustically Thick Films

we focus on a portion of the film that is small in lateral extent compared with the SAW wavelength. As the wave passes a fixed point, the lower surface of the film oscillates in response to the sinusoidal SAW surface displacement. If the film is acoustically thick (/7 1), the upper portions of the film tend to lag behind the driven substrate/film interface, inducing strains across the thickness of the film. This inertial deformation of the film results in nonuniform displacement across the film. 

From the aforementioned considerations, a perturbational formula can be derived for the SAW velocity and attenuation changes, applying to either acoustically thin or thick viscoelastic films [50]  

The response given by Equation 3.60 is largely determined by the phase shifts 0/ = Re Pih], where Re ) denotes die real part of the complex expression. For 

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